Sets the Task#mLaunchNextToBubble on leaf task vs. the root task

In Desktop mode, the Task is organized by a Desk root-task. Starting
the same task into bubble unexpectedly sets the Desk root-task's
`mLaunchNextToBubble` to `true`.

This CL also fixes a potential issue where the always-on-top could
be set on a created-by-organizer root-task.

Bug: 430687520
Test: start an app to Desktop, to background, start it again to bubble
Flag: EXEMPT bugfix
Change-Id: Ia0022cf2f4182b65dd1841055e72ae3ddac8364a